This invention relates to a vapor phase process for selective conversion of fluorodichloromethane (CHCl.sub.2 F) and carbon tetrachloride (CCl.sub.4) to fluorotrichloromethane (CCl.sub.3 F), difluorodichloromethane (CCl.sub.2 F.sub.2) and difluorochloromethane (CHClF.sub.2) and by-product chloroform (CHCl.sub.3) using a solid catalyst of an activated mixture of iron oxide and rare earth oxides.
Generally, fluorinated alkanes are produced commercially by liquid phase reaction of anhydrous hydrogen fluoride (HF) with chloroalkanes in the presence of a catalyst at superatmospheric pressure: Daudt et al., U.S. Pat. Nos. 2,005,705 and 2,005,708. This reaction is illustrated by the following equation using carbon tetrachloride as the representative haloalkane: ##STR1## wherein x is 1 to 3. A mixture of products is obtained; the amount of each product depends on process conditions and feed ratios. In the above illustration, the overfluorinated product, trifluorochloromethane (CClF.sub.3), is an undesired by-product whose vapor pressure is too high for significant commercial use and whose fluorine values are, therefore, usually wasted. Furthermore, the conventional process employs anhydrous HF, a particularly corrosive chemical which is very hazardous to handle. Hydrochloric acid (HCl) is a by-product and must be disposed of, either by considerable purification to eliminate residual halocarbons prior to sale, or by neutralization and disposal at significant expense and environmental risk. Finally, the antimony-based catalyst eventually loses both activity and selectivity, and must be disposed of with extreme caution because of environmental concerns relating particularly to possible contamination of surface and subsurface water.
French Patent No. 1,422,476 describes a catalyst for hydrofluorination of chlorocarbons to a range of fluorinated products. For example, anhydrous hydrofluoric acid is reacted with carbon tetrachloride in the vapor phase over an activated catalyst of iron and cerium oxides to form CCl.sub.3 F, CCl.sub.2 F.sub.2 and CClF.sub.3 and hydrochloric acid.
In U.S. Pat. No. 3,087,975, an activated alumina catalyst is disclosed for converting CCl.sub.2 F.sub.2 primarily to CClF.sub.3 and CCl.sub.4. Similarly, in U.S. Pat. No. 3,087,976, monohydrofluorochloromethanes with one or two fluorine atoms are converted primarily to trifluoromethane (CHF.sub.3) and CHCl.sub.3 over activated alumina.
It is the object of the present invention to selectively synthesize the fluorochloromethanes of primary commercial interest without loss to overfluorinated products of little or no commercial utility. More specifically, the object of the present invention is a process effective under mild conditions without hydrogen fluoride feed or hydrochloric acid by-product formation, and without a catalyst whose eventual disposal poses serious environmental concerns.